.TH funcinterval 8  "2020-05-27" "USER COMMANDS"
.SH NAME
funcinterval \- Time interval between the same function, tracepoint as a histogram.
.SH SYNOPSIS
.B funcinterval [\-h] [\-p PID] [\-i INTERVAL] [\-d DURATION] [\-T] [\-u] [\-m] [\-v] pattern
.SH DESCRIPTION
This tool times interval between the same function as a histogram.

eBPF/bcc is very suitable for platform performance tuning.
By funclatency, we can profile specific functions to know how latency
this function costs. However, sometimes performance drop is not about the 
latency of function but the interval between function calls.
funcinterval is born for this purpose.

This tool uses in-kernel eBPF maps for storing timestamps and the histogram,
for efficiency.

WARNING: This uses dynamic tracing of (what can be many) functions, an
activity that has had issues on some kernel versions (risk of panics or
freezes). Test, and know what you are doing, before use.

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
pattern
Function name.
\-h
Print usage message.
.TP
\-p PID
Trace this process ID only.
.TP
\-i INTERVAL
Print output every interval seconds.
.TP
\-d DURATION
Total duration of trace, in seconds.
.TP
\-T
Include timestamps on output.
.TP
\-u
Output histogram in microseconds.
.TP
\-m
Output histogram in milliseconds.
.TP
\-v
Print the BPF program (for debugging purposes).
.SH EXAMPLES
.TP
Time the interval of do_sys_open() kernel function as a histogram:
#
.B funcinterval do_sys_open
.TP
Time the interval of xhci_ring_ep_doorbell(), in microseconds:
#
.B funcinterval -u xhci_ring_ep_doorbell
.TP
Time the interval of do_nanosleep(), in milliseconds
#
.B funcinterval -m do_nanosleep
.TP
Output every 5 seconds, with timestamps:
#
.B funcinterval -mTi 5 vfs_read
.TP
Time process 181 only:
#
.B funcinterval -p 181 vfs_read
.TP
Time the interval of mm_vmscan_direct_reclaim_begin tracepoint:
#
.B funcinterval t:vmscan:mm_vmscan_direct_reclaim_begin
.TP
Time the interval of c:malloc used by top every 3 seconds:
#
.B funcinterval -p `pidof -s top` -i 3 c:malloc
.TP
Time /usr/local/bin/python main function:
#
.B funcinterval /usr/local/bin/python:main
.SH FIELDS
.TP
necs
Nanosecond range
.TP
usecs
Microsecond range
.TP
msecs
Millisecond range
.TP
count
How many calls fell into this range
.TP
distribution
An ASCII bar chart to visualize the distribution (count column)
.SH OVERHEAD
This traces kernel functions and maintains in-kernel timestamps and a histogram,
which are asynchronously copied to user-space. While this method is very
efficient, the rate of kernel functions can also be very high (>1M/sec), at
which point the overhead is expected to be measurable. Measure in a test
environment and understand overheads before use. You can also use funccount
to measure the rate of kernel functions over a short duration, to set some
expectations before use.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Edward Wu
.SH SEE ALSO
funclatency(8)
funccount(8)
